The present invention relates to a passive missile guidance process, particularly with a view to the interception by said missile of a target travelling at low altitude, and particularly above the sea.
Infrared homing of a missile on a target is known to be effected with excellent precision. However, such precision is attained only in the vicinity of the target, the range of the infrared homing heads not exceeding a few kilometers.
Provision must therefore be made to ensure take-over of a missile at a considerable distance from the target by electromagnetic guidance.
Now, the passive electromagnetic guidance of a missile at low altitude, of which the path must be slaved to a target therefore also travelling at low altitude, is rendered very difficult since the guidance processes at present carried out furnish guidance data in elevation which are all the more erroneous as the distance between the missile and the target decreases.
This comes from the fact that the missile guidance system receives not only the radiation directly emitted by the target, but also a radiation reflected on the surface of the sea and appearing to come from the optical image of the target with respect to this surface. When the target is travelling at low or very low altitude, very close to the surface of the sea, it is very difficult to discriminate the two radiations, with the result that the missile is then guided not on the target itself, but on an apparent target located at the intersection of the vertical of the target with the surface of the sea, i.e. projection of the target on this surface.